1. Field of the Invention
The present invention relates to a porous material suitable for use in a bearing retainer, obtained by a process comprising the steps of mixing degreased bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture obtained after the primary firing into carbonized powders sieved through a 60-mesh screen, mixing the carbonized powders with a thermosetting resin before kneading, pressure-forming a kneaded mixture thus obtained at a pressure in a range of 20 to 30 MPa, and applying a heat treatment again to a formed kneaded mixture in the inert gas at a temperature in a range of 100 to 1100xc2x0 C.
2. Description of the Related Art
Glass-fiber reinforced polyamide such as Nylon 66 reinforced by glass fiber, metal, and so forth have been in widespread use up to now as material for a retainer of bearings such as ball bearings, taper bearings, and so forth. As a lubricating oil such as oil, grease, and the like is used for these bearings, a hot-oil-resistant Nylon 66 blended with a lubricating-oil resistant-stabilizer has been used for Nylon 66 for use in retainers.
However, even such a hot-oil-resistant Nylon 66 has been unable to withstand applications thereof at a high temperature on a long term basis, and accordingly, various improvements have been attempted.
Meanwhile, an attempt to obtain a porous carbonaceous material by utilizing rice bran, discharged in quantity of 90,000 tons a year in Japan, and as much as 33 million tons throughout the world, has been well known by researches carried out by Mr. Kazuo HOEKIRIGAWA, the first inventor of the present invention (refer to xe2x80x9cFunctional Materialxe2x80x9d, May issue, 1997, Vol. 17, No. 5, pp. 24xcx9c28).
Herein are disclosed a carbonaceous material obtained by mixing and kneading degreased bran derived from rice bran with a thermosetting resin, drying a formed kneaded mixture prepared by pressure-forming, and fang the formed kneaded mixture as dried in an inert gas, and a method of forming the same.
With such a method as described above, however, it has been practically difficult to form the formed kneaded mixture with precision because there occurs discrepancy in dimensions by as much as 25% in terms of a contraction ratio of the dimensions of the formed kneaded mixture prepared by the pressure-forming to those of a finished formed product obtained after the firing in the inert gas.
The invention has been developed to solve the problem described above, and it is therefore an object of the invention to provide a porous material suitable for use in a bearing retainer, having such properties as a small contraction ratio of the dimensions of a formed workpiece to those of a finished product, excellent hot oil resistance, small thermal strain, insusceptibility to damage, light weight, a long service life, and ability to retain oil and grease for a long period of time, thereby providing a high-tech eco-material (state-of-the-art material excellent in ecological adaptability) utilizing biomass resources, different from conventional industrial material.
The inventors have been successful in development of a porous material suitable for use in fabricating a high-precision bearing retainer, having excellent properties as a material for use in fabricating a bearing retainer, and a small contraction ratio of the dimensions of a formed workpiece to those of a finished product.
The inventor of the present invention has conducted intense studies, and found out that a porous material is obtained by a process comprising the steps of mixing degreased bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture obtained after the primary firing into carbonized powders sieved through a 60-mesh screen, mixing the carbonized powders with a thermosetting resin before kneading, pressure-forming a kneaded mixture thus obtained at a pressure in a range of 20 to 30 MPa, and applying a heat treatment again to a formed kneaded mixture in the inert gas at a temperature in a range of 100 to 1100xc2x0 C., and the porous material thus obtained has not only ideal properties as a material suitable for use in a bearing retainer but also a small contraction ratio of the dimensions of a formed workpiece to those of a finished product.
More specifically, the porous material described above has the contraction ratio of the dimensions of the formed workpiece to those of the finished product as low as 3% or less, 13 wt % of oil retention characteristic, 4.85xc3x9710xe2x88x923 xcexa9cm of volume resistivity, and density in a range of 1.05 to 1.3 g/cm3, and further, it has been possible to obtain the porous material having suitable hardness, and still friction coefficient in the order of about 1. 05 after fired at a high temperature.